Light-emitting device having light-emitting elements

ABSTRACT

A light-emitting device operating on a high drive voltage and a small drive current. LEDs ( 1 ) are two-dimensionally formed on an insulating substrate ( 10 ) of e.g., sapphire monolithically and connected in series to form an LED array. Two such LED arrays are connected to electrodes ( 32 ) in inverse parallel. Air-bridge wiring ( 28 ) is formed between the LEDs ( 1 ) and between the LEDs ( 1 ) and electrodes ( 32 ). The LED arrays are arranged zigzag to form a plurality of LEDs ( 1 ) to produce a high drive voltage and a small drive current. Two LED arrays are connected in inverse parallel, and therefore an AC power supply can be used as the power supply.

TECHNICAL FIELD

The present invention relates to a light emitting device in which aplurality of light emitting elements are formed on a substrate.

BACKGROUND ART

When light emitting means such as a light emitting element (LED) is usedfor display or the like, typical usage conditions are approximately 1 Vto 4 V for the drive voltage and approximately 20 mA for the drivecurrent. With the recent development of short-wavelength LEDs which usesa GaN-based compound semiconductor and commercialization of solid lightsources of full color, white color, etc., application of LEDs forillumination purposes has been considered. When an LED is used forillumination, there may be cases in which the LED is used underconditions other than the above-described conditions of 1 V-4 V of drivevoltage and 20 mA of drive current. As a result, steps have been takento enable a larger current to flow through the LED and to increase thelight emission output. In order to flow a larger current, an area of apn junction of the LED must be increased so that the current density isreduced.

When the LED is used as a light source for illumination, it isconvenient to use an AC power supply and allow use with a drive voltageof 100 V or greater. In addition, if the same light emission output isto be obtained with supply of the same power, the power loss can bereduced by applying a high voltage while maintaining a low currentvalue. In the LEDs of the related art, however, it is not alwayspossible to sufficiently increase the drive voltage.

DISCLOSURE OF INVENTION

An object of the present invention is to provide a light emitting devicewhich can be operated with a high drive voltage.

According to one aspect of the present invention, there is provided alight emitting device wherein a plurality of GaN-based light emittingelements are formed on an insulating substrate and the plurality oflight emitting elements are monolithically formed and connected inseries.

According to another aspect of the present invention, it is preferablethat, in the light emitting device, the plurality of light emittingelements are arranged on the substrate in a two-dimensional pattern.

According to another aspect of the present invention, it is preferablethat, in the light emitting device, the plurality of light emittingelements are grouped into two groups and the two groups are connectedbetween two electrodes in parallel so that the two groups are ofopposite polarities.

According to another aspect of the present invention, it is preferablethat, in the light emitting device, the plurality of light emittingelements are connected by air bridge lines.

According to another aspect of the present invention, it is preferablethat, in the light emitting device, the plurality of light emittingelements are electrically separated by sapphire which is used as thesubstrate.

According to another aspect of the present invention, it is preferablethat, in the light emitting device, the plurality of light emittingelements are grouped into two groups having equal numbers of lightemitting elements, an array of light emitting elements in each group arearranged in a zigzag pattern, and the two groups of light emittingelement arrays are connected between two electrodes in parallel so thatthey are of opposite polarities. According to another aspect of thepresent invention, it is preferable that, in the light emitting device,the two groups of light emitting element arrays are arrangedalternately.

According to another aspect of the present invention, it is preferablethat, in the light emitting device, the light emitting element and theelectrode have a planar shape of approximate square or triangle.

According to another aspect of the present invention, it is preferablethat, in the light emitting device, the overall shape of the pluralityof light emitting elements and the electrode is approximate square.

According to another aspect of the present invention, it is preferablethat, in the light emitting device, the electrode is an electrode for analternate current power supply.

According to another aspect of the present invention, it is preferablethat, in the light emitting device, the two groups of light emittingelement arrays have a common n electrode.

In the present invention, a plurality of light emitting elements aremonolithically formed, that is, formed on a same substrate, and areconnected in series. With this structure, the present invention allows ahigh drive voltage. By connecting a plurality of light emitting elementsalong one direction, a DC drive is possible. By grouping the pluralityof light emitting elements into two groups and connecting the two groupsbetween electrodes such that the two groups of light emitting elements(light emitting element arrays) are of opposite polarities from eachother, it is possible to also allow an AC drive. The numbers of elementsin the groups may be the same or different.

Various methods are available for two-dimensionally placing or arranginga plurality of light emitting elements, and a method which minimizes anarea occupied on the substrate is desirable. For example, by arrangingthe two groups of light emitting element arrays in zigzag pattern, thatis, arranging a plurality of light emitting elements on a bent line andalternately arranging the light emitting element arrays, the substratearea can be efficiently utilized and a large number of light emittingelements can be connected. When the two light emitting element arraysare alternately positioned, a crossing portion of lines may occur. It ispossible to effectively prevent short-circuiting at the crossing portionby connecting the light emitting elements by air bridge lines. Theshapes of the light emitting elements and the electrodes is not limited.By forming the light emitting elements and the electrodes to have aplanar shape of, for example, approximate square, the overall shapebecomes an approximate square, which allows for the use of a standardmounting structure. It is also possible to employ a shape other than thesquare, for example, a triangle, for the light emitting elements and theelectrodes, to form an approximate square shape as an overall shape bycombining the triangles, and, as a consequence, it is possible to use astandard mounting structure in a similar manner.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing a basic structure of a light emittingelement (LED).

FIG. 2 is an equivalent circuit diagram of a light emitting device.

FIG. 3 is a plan view of two LEDs.

FIG. 4 is a crosssectional view along a IV-IV line of FIG. 3.

FIG. 5 is another equivalent circuit diagram of a light emitting device.

FIG. 6 is an explanatory diagram of a structure in which 40 LEDs arearranged in a two-dimensional pattern.

FIG. 7 is a circuit diagram of the structure shown in FIG. 6.

FIG. 8 is an explanatory diagram of a structure in which 6 LEDs arearranged in a two-dimensional pattern.

FIG. 9 is a circuit diagram of the structure shown in FIG. 8.

FIG. 10 is an explanatory diagram of a structure in which 14 LEDs arearranged in a two-dimensional pattern.

FIG. 11 is a circuit diagram of the structure shown in FIG. 10.

FIG. 12 is an explanatory diagram of a structure in which 6 LEDs arearranged in a two-dimensional pattern.

FIG. 13 is a circuit diagram of the structure shown in FIG. 12.

FIG. 14 is an explanatory diagram of a structure in which 16 LEDs arearranged in a two-dimensional pattern.

FIG. 15 is a circuit diagram of the structure shown in FIG. 14.

FIG. 16 is an explanatory diagram of a structure comprising 2 LEDs.

FIG. 17 is a circuit diagram of the structure shown in FIG. 16.

FIG. 18 is an explanatory diagram of a structure in which 4 LEDs arearranged in a two-dimensional pattern.

FIG. 19 is a circuit diagram of the structure shown in FIG. 18.

FIG. 20 is an explanatory diagram of a structure in which 3 LEDs arearranged in a two-dimensional pattern.

FIG. 21 is a circuit diagram of the structure shown in FIG. 20.

FIG. 22 is an explanatory diagram of a structure in which 6 LEDs arearranged in a two-dimensional pattern.

FIG. 23 is a circuit diagram of the structure shown in FIG. 22.

FIG. 24 is an explanatory diagram of a structure in which 5 LEDs arearranged in a two-dimensional pattern.

FIG. 25 is a circuit diagram of the structure shown in FIG. 24.

FIG. 26 is an explanatory diagram of another two-dimensionalarrangement.

FIG. 27 is a circuit diagram of the structure shown in FIG. 26.

FIG. 28 is an explanatory diagram of another two-dimensionalarrangement.

FIG. 29 is a circuit diagram of the structure shown in FIG. 28.

FIG. 30 is an explanatory diagram of another two-dimensionalarrangement.

FIG. 31 is a circuit diagram of the structure shown in FIG. 30.

BEST MODE FOR CARRYING OUT THE INVENTION

A preferred embodiment of the present invention will now be describedreferring to the drawings.

FIG. 1 shows a basic structure of an LED 1 which is a GaN-based compoundsemiconductor light emitting element of the present embodiment. The LED1 has a structure in which a GaN layer 12, an Si-doped n-type GaN layer14, an InGaN light emitting layer 16, an AlGaN layer 18, and a p-typeGaN layer 20 are sequentially layered on a substrate 10, a p electrode22 is formed in contact with the p-type GaN layer 20, and an n electrode24 is formed in contact with the n-type GaN layer 14.

The LED shown in FIG. 1 is manufactured through the following process.First, a sapphire c-plane substrate is thermally treated for 10 minutesin a hydrogen atmosphere at a temperature of 1100° C. in an MOCVDdevice. Then, the temperature is reduced to 500° C. and silane gas andammonia gas are supplied for 100 seconds to form a discontinuous SiNfilm on the substrate 10. This process is applied in order to reduce adislocation density within the device and the SiN film is not shown inFIG. 1. Next, trimethyl gallium and ammonia gas are supplied at the sametemperature to grow a GaN layer to a thickness of 20 nm. The temperatureis raised to 1050° C. and trimethyl gallium and ammonia gas are suppliedagain to grow an undoped GaN (u-GaN) layer 12 and an Si-doped n-type GaNlayer 14 to a thickness of 2 μm each. Then, the temperature is reducedto approximately 700° C. and an InGaN light emitting layer 16 is grownto a thickness of 2 nm. A target composition is x=0.15, that is,In_(0.15)Ga_(0.85)N. After the light emitting layer 16 is grown, thetemperature is raised to 1000° C., an AlGaN hole injection layer 18 isgrown, and a p-type GaN layer 20 is grown.

After the p-type GaN layer 20 is grown, the wafer is taken out of theMOCVD device and a Ni layer of 10 nm and a Au layer of 10 nm aresequentially vacuum-evaporated to form these layers on the surface ofthe grown layer. A thermal treatment is applied in a nitrogen gasatmosphere containing 5% oxygen at a temperature of 520° C. so that themetal film becomes a p-type transparent electrode 22. After thetransparent electrode is formed, a photoresist is applied over theentire surface and an etching process is applied for forming an n-typeelectrode using the photoresist as a mask. The depth of etching is, forexample, approximately 600 nm. A Ti layer of 5 nm thickness and an Allayer of 5 nm thickness are formed above the n-type GaN layer 14 exposedby the etching process and a thermal treatment is applied in a nitrogengas atmosphere at a temperature of 450° C. for 30 minutes to form ann-type electrode 24. Finally, a rearside of the substrate 10 is groundto a thickness of 100 μm and chips are cut away and mounted to obtainthe LED 1.

In FIG. 1, one GaN-based LED 1 is formed on a substrate 1, but in thepresent embodiment, a plurality of LEDs 1 are monolithically formed onthe substrate 10 in a two-dimensional array and the LEDs are connectedto form the light emitting device (chip). Here, “monolithic” indicatesthat all elements are formed on one single substrate.

FIG. 2 is a diagram showing an equivalent circuit of the light emittingdevice. In FIG. 2, the light emitting elements formed in thetwo-dimensional array are grouped into two groups of same number oflight emitting elements (in FIG. 2, 4 light emitting elements). The LEDs1 in each group are connected in series and the two groups of LED arraysare connected in parallel between electrodes (drive electrodes) suchthat the two groups are of opposite polarities. In this manner, byconnecting the array of LEDs in series, it is possible to drive the LEDs1 at a high voltage in which the drive voltage of each LED is added.Because the LED arrays are connected in parallel between the electrodessuch that the LED arrays are of opposite polarities, even when an ACpower supply is used as a power supply, one of the LED array alwaysemits light in each period of the power supply, which allows aneffective light emission.

FIG. 3 is a partial plan view of a plurality of LEDs monolithicallyformed on the substrate 10. FIG. 4 is a diagram showing a IV-IV crosssection of FIG. 3. In FIG. 3, a p electrode 22 and an n electrode 24 areformed on the upper surface of the LED 1 as shown in FIG. 1. The pelectrode 22 and the n electrode 24 of adjacent LEDs 1 are connectedthrough an air bridge line 28 and a plurality of LEDs 1 are connected inseries.

In FIG. 4, the LEDs 1 are shown in a simple manner for explanationpurposes. Specifically, only the n-GaN layer 14, the p-GaN layer 20, thep-electrode 22, and the n-electrode 24 are shown. In real applications,the InGaN light emitting layer 16 is also present as shown in FIG. 1.The air bridge line 28 connects from the p electrode 22 to the nelectrode 24 through the air. In this manner, in contrast to a method ofapplying an insulating film on a surface of the element, formingelectrodes on the insulating film, and electrically connecting the pelectrode 22 and the n electrode 24, it is possible to avoid the problemof degradation of the LEDs 1 as a result of thermal diffusion ofelements forming the insulating material to the n layer and p layer froma line disconnection or insulating film, because it is no longernecessary to place the electrodes along the etching groove. The airbridge line 28 is also used for connecting between the LED 1 and theelectrode which is not shown in FIG. 4, in addition to the connectionbetween the LEDs 1.

In addition, as shown in FIG. 4, the LEDs 1 must be independent andelectrically insulated from each other. For this purpose, the LEDs 1 areseparated on the sapphire substrate 10. Because sapphire is aninsulating material, it is possible to electrically separate the LEDs 1.By using the sapphire substrate 10 as a resistive body for achieving anelectrical separation between the LEDs, it is possible to electricallyseparate the LEDs in an easy and reliable manner.

As the light emitting element, it is also possible to employ an MIS inplace of the LED having a pn junction.

FIG. 5 is a diagram showing another equivalent circuit of the lightemitting device. In FIG. 5, 20 LEDs 1 are connected in series to formone LED array and two such LED arrays (a total of 40 LEDs) are connectedto a power supply in parallel. The drive voltage of the LED 1 is set to5 V, and thus, the drive voltage of each LED array is 100 V. The two LEDarrays are connected in parallel to the power supply such that the LEDarrays are of opposite polarities, similar to FIG. 2. Light is alwaysemitted from one of the LED arrays, regardless of the polarity of thepower supply.

FIG. 6 shows a specific structure of the two-dimensional array andcorresponds to the equivalent circuit diagram of FIG. 2. In FIG. 6, atotal of 40 LEDs 1 are formed on the sapphire substrate 10 which aregrouped into two groups of 20 LEDs 1. The groups of LEDs 1 are connectedin series by the air bridges 28 to form two LED arrays. Morespecifically, all of the LEDs 1 has a square shape of the same size andsame shape. A first LED array comprises, from the top line toward thebottom line, a line of 6 LEDs are arranged in a straight line, a line of7 LEDs are arranged in a straight line, and a line of 7 LEDs arearranged in a straight line. The first row (6 LEDs) and the second row(7 LEDs) are formed facing opposite directions and the second row andthe third row are formed facing opposite directions. The first row andthe second row are separated from each other and the second row and thethird row are separated from each other, because rows of the other LEDarray are alternately inserted, as will be described later. Therightmost LED 1 of the first row and the rightmost LED 1 of the secondrow are connected by an air bridge line 28 and the leftmost LED 1 of thesecond row and the leftmost LED 1 of the third row are connected by anair bridge line 28 to construct a zigzag arrangement. The leftmost LED 1of the first row is connected to an electrode (pad) 32 formed on anupper left section of the substrate 10 by an air bridge line 28 and therightmost LED 1 of the third row is connected to an electrode (pad) 32formed on a lower right section of the substrate 10 by an air bridgeline 28. The two electrodes (pads) 32 have the same square shape as theLEDs 1. The second LED array is alternately formed in the spaces of thefirst LED array. More specifically, in the second LED array, 7 LEDs, 7LEDs, and 6 LEDs are formed on straight lines from the top to thebottom, the first row is formed between the first row and the second rowof the first LED array, the second row is formed between the second rowand the third row of the first LED array, and the third row is formedbelow the third row of the first LED array. The first row and the secondrow of the second LED array are formed facing opposite directions andthe second row and the third row of the second LED array are formedfacing opposite directions. The rightmost LED 1 of the first row isconnected to the rightmost LED 1 of the second row by an air bridge line28 and the leftmost LED 1 of the second row is connected to the leftmostLED 1 of the third row by an air bridge line 28 to construct a zigzagarrangement. The leftmost LED of the first row of the second LED arrayis connected to the electrode 32 formed on the upper left section of thesubstrate 10 by an air bridge line 28 and the rightmost LED 1 of thethird row is connected to the electrode 32 formed on the lower rightsection of the substrate 10 by an air bridge line 28. Polarities of theLED arrays with respect to the electrodes 32 are opposite from eachother. The overall shape of the light emitting device (chip) isrectangular. It should also be noted that two electrodes 32 to which apower supply is supplied are formed in diagonally opposite positions ofthe rectangle and are spaced apart.

FIG. 7 is a circuit diagram of the circuit shown in FIG. 6. It can beseen from this figure that each LED array is connected in series whilebending in a zigzag pattern and two LED arrays have the zigzag shapedrows formed between the rows of the other LED array. By employing such aconfiguration, many LEDs 1 can be arranged on a small substrate 10. Inaddition, because only two electrodes 32 are required for 40 LEDs 1, theusage efficiency on the substrate 10 can be further improved. Moreover,when the LEDs 1 are individually formed in order to separate LEDs 1, thewafer must be cut for separation, but, in the present embodiment, theseparation between LEDs 1 can be achieved through etching, which allowsfor narrowing of a gap between the LEDs 1. With this configuration, itis possible to further reduce the size of the sapphire substrate 10. Theseparation between LEDs 1 is achieved by etching and removing regionsother than the LEDs 1 to the point which reaches the substrate 10 byusing photoresist, reactive ion etching, and wet etching. Because theLED arrays alternately emit light, the light emission efficiency can beimproved and heat discharging characteristic can also be improved.Moreover, by changing the number of LEDs 1 to be connected in series,the over all drive voltage can also be changed. In addition, by reducingthe area of the LED 1, it is possible to increase the drive voltage perLED. When 20 LEDs 1 are serially connected and are driven with acommercially available power supply (100 V, 60 Hz), a light emissionpower of approximately 150 mW can be obtained. The drive current in thiscase is approximately 20 mA.

As is clear from FIG. 7, when two LED arrays are alternately arranged ina zigzag pattern, a crossing section 34 inevitably occurs in the airbridge line 28. For example, when the first row and the second row ofthe second LED array are connected, this portion crosses the lineportion for connecting the first row and the second row of the first LEDarray. However, the air bridge line 28 of the present embodiment is notadhered to the substrate 10 as described above and extends through theair, distanced from the substrate 10. Because of this structure,short-circuiting due to contact of the air bridge lines 28 at thecrossing section can be easily avoided. This is one advantage of usingthe air bridge line 28. The air bridge line 28 is formed, for example,through the following processes. A photoresist is applied over theentire surface to a thickness of 2 μm and a post bake process is appliedafter a hole is opened in a shape of the air bridge line. Over thisstructure, a Ti layer of 10 nm and a Au layer of 10 nm are evaporated inthis order through vacuum evaporation. A photoresist is again appliedover the entire surface to a thickness of 2 μm and holes are opened inportions in which the air bridge lines are to be formed. Then, using Tiand Au as electrodes, Au is deposited over the entire surface of theelectrodes to a thickness of 3-5 μm through ion plating (plating) in anelectrolyte. Then, the sample is immersed in acetone, the photoresist isdissolved and removed through ultrasonic cleaning, and the air bridgeline 28 is completed.

In this manner, by placing the plurality of LEDs 1 in a two-dimensionalarray shape, it is possible to effectively use the substrate area and toallow a high drive voltage, in particular, driving using thecommercially available power supply. Various other patterns can beemployed as the pattern of the two-dimensional array. In general, thetwo-dimensional array pattern preferably satisfies the followingconditions:

-   (1) the shape of the LED and electrode positions are preferably    identical in order to allow uniform current to flow through the LEDs    and to obtain uniform light emission;-   (2) the sides of the LEDs are preferably straight lines in order to    allow cutting of wafer to create chips;-   (3) the LED preferably has a planar shape similar to square in order    to use a standard mount and utilize reflection from periphery to    improve the light extraction efficiency;-   (4) a size of two electrodes (bonding pads) is preferably    approximately 100 μm square and the two electrodes are preferably    separated from each other; and-   (5) the ratio of the line and pad is preferably minimum in order to    effectively use the wafer area.

These conditions are not mandatory, and it is possible, for example, toemploy a planar shape of triangle as the shape of the LED. Even when theshape of the LED is a triangle, the overall shape of approximate squarecan be obtained by combining the triangles. Some examples oftwo-dimensional array patterns will now be described.

FIG. 8 shows a two-dimensional arrangement of a total of 6 LEDs 1 andFIG. 9 shows a circuit diagram of this configuration. The arrangement ofFIG. 8 is basically identical to that of FIG. 6. 6 LEDs are grouped intotwo groups of the same number to form LED arrays having 3 LEDs connectedin series. The first LED array is arranged in a zigzag pattern with thefirst row having one LED and the second row having two LEDs. The LED ofthe first row and the rightmost LED 1 of the second row are connected inseries by an air bridge line 28 and the two LEDs 1 of the second row areconnected in series by an air bridge line 28. Electrodes (pads) 32 areformed at an upper left section and a lower left section of thesubstrate 10. The LED 1 of the first row is connected to the electrode32 at the upper left section by an air bridge line and the leftmost LED1 of the second row is connected to the electrode 32 at the lower leftsection. The second LED array is also arranged in a zigzag pattern andhas two LEDs 1 on the first row and one LED 1 on the second row. Thefirst row of the second LED array is formed between the first row andthe second row of the first LED array and the second row of the secondLED array is formed below the second row of the first LED array. Therightmost LED 1 of the first row is connected in series to the LED 1 ofthe second row by an air bridge line 28 and the two LEDs 1 on the firstrow are connected in series by an air bridge line 28. The leftmost LED 1of the first row is connected to the electrode 32 at the upper leftsection by an air bridge line 28 and the LED 1 of the second row isconnected to the electrode 32 at the lower left section by an air bridgeline 28. As can be seen from FIG. 9, in this configuration also, two LEDarrays are connected between the electrodes 32 in parallel such thatthey are of opposite polarities. Therefore, when an AC power supply issupplied, the two LED arrays alternately emit light.

FIG. 10 shows a configuration in which a total of 14 LEDs are arrangedin a two-dimensional pattern and FIG. 11 shows a circuit diagram of thisconfiguration. 14 LEDs are grouped into two groups and the LED array has7 LEDs connected in series. A first LED array is arranged in a zigzagpattern with the first row having 3 LEDs 1 and the second row having 4LEDs 1. The leftmost LED of the first row and the leftmost LED 1 of thesecond row are connected in series by an air bridge line 28, 3 LEDs ofthe first row are connected in series by air bridge lines 28, and 4 LEDs1 of the second row are connected in series by air bridge lines 28.Electrodes (pads) 32 are formed at an upper right section and a lowerright section of the substrate 10, the rightmost LED 1 of the first rowis connected to the electrode 32 at the upper right section by an airbridge line and the rightmost LED 1 of the second row is connected tothe electrode 32 at the lower right section. A second LED array also isarranged in a zigzag pattern with a first row having 4 LEDs 1 and asecond row having 3 LEDs 1. The first row of the second LED array isformed between the first row and the second row of the first LED arrayand the second row of the second LED array is formed below the secondrow of the first LED array. The leftmost LED 1 of the first row isconnected in series to the leftmost LED 1 of the second row by an airbridge line 28. 4 LEDs 1 on the first row are connected in series and 3LEDs 1 on the second row are connected in series. The rightmost LED 1 onthe first row is connected to the electrode 32 on the upper rightsection by an air bridge line 28 and the rightmost LED 1 on the secondrow is connected to the electrode 32 at the lower right section by anair bridge line 28. As can be seen from FIG. 11, in this configurationalso, the two LED arrays are connected between the electrodes 32 inparallel such that they are of opposite polarities. Therefore, when anAC-power supply is supplied, the two LED arrays alternately emit light.

Characteristics common to the two-dimensional patterns of FIGS. 6, 8,and 10 are that the LEDs 1 have the same shape of approximate square andsame size, the two electrodes (pads) also have approximate square shapeand are not formed adjacent to each other (are formed separate from eachother), the configuration is a combination of two LED arrays, the twoLED arrays are bent and cross each other on the chip, the two LED arraysare connected between electrodes such that they are of oppositepolarities, etc.

FIG. 12 shows a configuration in which LEDs having a planar shape oftriangle are arranged in a two-dimensional pattern and FIG. 13 shows acircuit diagram of this configuration. In FIG. 12, a total of 6 LEDs,LEDs 1 a, 1 b, 1 c, 1 d, 1 e, and if are formed such that they have aplanar shape of a triangle. LEDs 1 a and 1 e are arranged opposing eachother at one side of the triangle so that the two LEDs form anapproximate square and LEDs 1 b and 1 f are placed opposing each other,so that the two LEDs form an approximate square. The LED 1 d and anelectrode 32 oppose and are connected to each other and the LED 1 c andan electrode 32 oppose and are connected to each other. Similar to theLEDs, the two electrodes 32 also have a planar shape of a triangle andare placed to form an approximate square. The opposing sides of the LEDsform an n electrode 24, that is, two opposing LEDs share the n electrode24. Similarly, the LED and the electrode 32 are connected through the nelectrode. In this arrangement also, the 6 LEDs are grouped into twogroups similar to the above-described arrangements. A first LED arrayincludes the LEDs 1 a, 1 b, and 1 c. A p electrode 22 of the LED 1 a isconnected to the electrode 32 by an air bridge line 28 and an nelectrode 24 of the LED 1 a is connected to a p electrode 22 of the LED1 b by an air bridge line 28. An n electrode 24 of the LED 1 b isconnected to a p electrode 22 of the LED 1 c by an air bridge line 28.An n electrode 24 of the LED 1 c is connected to the electrode 32. Asecond LED array includes LEDs 1 d, 1 e, and 1 f. The electrode 32 isconnected to a p electrode 22 of the LED 1 f by an air bridge line 28,an n electrode 24 of the LED 1 f is connected to a p electrode 22 of theLED 1 e by an air bridge line 28, an n electrode 24 of the LED 1 e isconnected to a p electrode 22 of the LED 1 d by an air bridge line 28,and an n electrode 24 of the LED 1 d is connected to the electrode 32.

In FIG. 13, it should also be noted that the n electrode of the LED 1 awhich is a part of the first LED array is connected to the n electrodeof the LED 1 e which is a part of the second LED array and the nelectrode of the LED 1 b which is a part of the first LED array isconnected to the n electrode of the LED 1 f which is a part of thesecond LED array. By sharing some of the n electrodes in the two LEDarrays, it is possible to reduce the amount of circuit wiring. Inaddition, in this configuration also, the two LED arrays are connectedbetween the electrodes 32 in parallel such that they are of oppositepolarities. The LEDs have the same shape and the same size, and byplacing the LEDs to oppose at one side and forming the electrode 32 in atriangular shape, it is possible to densely form the LEDs and electrodesto reduce the necessary area of the substrate.

FIG. 14 shows another configuration in which LEDs having a planar shapeof a triangle are arranged in a two-dimensional pattern and FIG. 15shows a circuit diagram of this configuration. In this configuration, atotal of 16 LEDs, LEDs 1 a-1 r are two-dimensionally formed. LEDs 1 aand 1 j, LEDs 1 b and 1 k, LEDs 1 c and 1 m, LEDs 1 d and 1 n, LEDs 1 eand 1 p, LEDs 1 f and 1 q, and LEDs 1 g and 1 r oppose each other at oneside of the triangle. An n electrode 24 is formed common to the LEDs atthe opposing side. The LED 1 i and an electrode 32 oppose each other andthe LED 1 h and an electrode 32 oppose each other. A first LED arrayincludes the LEDs 1 a, 1 b, 1 c, 1 d, 1 e, 1 f, 1 g, and 1 h and asecond LED array includes the LEDs 1 r, 1 q, 1 p, 1 n, 1 m, 1 k, 1 j,and 1 i. An n electrode 24 of the LED 1 b is connected to a p electrode22 of the LED 1 c by an air bridge line 28 and an n electrode 24 of theLED 1 e is connected to a p electrode 22 of the LED 1 f by an air bridgeline 28. An n electrode 24 of the LED 1 q is connected to a p electrode22 of the LED 1 p by an air bridge line 28 and an n electrode of the LED1 m is connected to a p electrode 22 of the LED 1 k by an air bridgeline 28. In FIG. 14 also, a crossing portion occurs similar to FIG. 12,but short-circuiting can be avoided by the air bridge lines 28. In thisconfiguration also, some of the n electrodes 24 in the two LED arraysare formed as common structures in order to reduce the amount ofnecessary wirings. Moreover, in this configuration also, the two LEDarrays are connected between the electrodes 32 in parallel so that theyare of opposite polarities and the device can be AC driven. FIG. 12shows a case of 6 LEDs and FIG. 14 shows a case of 16 LEDs. Similartwo-dimensional arrangements can be achieved also with different numbersof LEDs. The present inventors have created a light emitting device inwhich 38 LEDs are arranged in a two-dimensional pattern.

Cases of AC drive have been described, but the structure can also be DCdriven. In this case, the LED arrays are not connected between theelectrodes to have opposite polarities, but rather, the LED array isconnected in a forward direction along the direction of polarity of theDC power supply. By connecting a plurality of LEDs in series, it ispossible to achieve a high voltage drive. Configurations for DC drivewill now described.

FIG. 16 shows a configuration in which two LEDs are connected in seriesand FIG. 17 shows a circuit diagram of this configuration. Each LED 1has a planar shape of a rectangle and an air bridge line 28 connectsbetween two LEDs. An electrode 32 is formed near each LED 1 and theelectrode 32 and the LED 1 form a rectangular region. In other words,the electrode 32 occupies a portion of the rectangular region and theLED 1 is formed in the other portion in the rectangular region.

FIG. 18 shows a configuration in which 4 LEDs are arranged in atwo-dimensional pattern and FIG. 19 shows a circuit diagram of thisconfiguration. In this configuration, each of the LEDs 1 of FIG. 16 isdivided into two LEDS and the two LEDs are connected in parallel. Thisconfiguration can also be described as two LED arrays each of which ismade of two LEDs connected in parallel in the forward direction. TheLEDs 1 a and 1 b form one LED array and the LEDs 1 c and 1 d formanother LED array. The LEDs 1 a and 1 c share a p electrode 22 and an nelectrode 24 and LEDs 1 b and 1 d also share a p electrode 22 and an nelectrode 24. With this configuration, there is an advantage in that thecurrent is more uniform compared to the configuration of FIG. 16.

FIG. 20 shows a configuration in which three LEDs are arranged in atwo-dimensional pattern and FIG. 21 shows a circuit diagram of thisconfiguration. LEDs 1 a, 1 b, and 1 c do not have the same shape and anelectrode 32 is formed in a portion of the LED 1 a. An n electrode 24 ofthe LED 1 a is connected to a p electrode of the LED 1 b by an airbridge line 28 striding over the LED 1 b. By devising the shape andarrangement of the LEDs, even with 3 LEDs, the overall outer shape ofthe light emitting device (chip) can be formed in an approximate square.

FIG. 22 shows a configuration in which a total of 6 LEDs are arranged ina two-dimensional pattern and FIG. 23 shows a circuit diagram of thisconfiguration. The LEDs 1 a-1 f have the same shape and same size andare, connected in series. The LEDs 1 a-1 c are placed on a straight lineand the LEDs 1 d-1 f are placed on another straight line. The LEDs 1 cand 1 d are connected by an air bridge line 28. In this configurationalso, the overall shape of the chip can be made approximate square.

FIG. 24 shows a configuration in which a total of 5 LEDs are arranged ina two-dimensional pattern and FIG. 25 shows a circuit diagram of thisconfiguration. LEDs 1 a-1 e have the same shape (rectangle) and the samesize. In this configuration also, the overall shape can be madeapproximate square.

A preferred embodiment of the present invention has been described. Thepresent invention is not limited to the preferred embodiment and variousmodifications can be made. In particular, the pattern when a pluralityof light emitting elements (LED or the like) are arranged in atwo-dimensional pattern may be patterns other than the ones describedabove. In this case, it is preferable to share electrodes betweenadjacent light emitting elements to reduce the amount of wiring, formthe overall shape in square or rectangle, connect a plurality of groupsof light emitting element arrays between electrodes in parallel, arrangethe plurality of light emitting element arrays in opposite polaritieswhen AC driven, combine the plurality of groups of light emittingelement arrays by bending the light emitting element arrays in a zigzagpattern, etc.

FIGS. 26-31 exemplify some of these alternative configurations. FIG. 26shows a two-dimensional arrangement in an example employing AC drive ofa total of 40 LEDs. FIG. 27 is a circuit diagram of this configuration.The configuration of FIG. 26 differs from that of FIG. 6 in that some ofthe two groups of LED arrays share the n electrode 24 (refer to FIG. 5).For example, an n electrode 24 of a second LED from the right of thefirst row of the first LED array (shown in the figure by α) is shared asthe n electrode 24 of the rightmost LED of the first row of the secondLED array (shown in the figure by β). Air bridge lines 28 at the ends ofthe LED arrays (shown in the figure by γ) are commonly formed withoutcrossing.

FIG. 28 shows a two-dimensional arrangement in a configuration employingAC drive and a total of 14 LEDs. FIG. 29 is a circuit diagram of thisconfiguration. The configuration of FIG. 28 differs from that of FIG. 10in that some of the two groups of LED arrays share the n electrode 24.For example, an n electrode 24 of the leftmost LED on a first row of afirst LED array (shown in the FIG. by α) is shared as an n electrode 24of an LED located second from the right on a first row of a second LEDarray (shown in the figure by β). Air bridge lines 28 at the ends (shownin the figure by γ) are commonly formed.

FIG. 30 shows a two-dimensional arrangement in a configuration employingAC drive and a total of 6 LEDs. FIG. 31 is a circuit diagram of thisconfiguration. In this configuration also, air bridge lines 28 at theends (γ portion) are commonly formed. It can be considered that in thisconfiguration also, an n electrode 24 in the first LED array and an nelectrode 24 of the second LED array are shared.

1. A light emitting device comprising a plurality of GaN-based lightemitting elements formed on an insulating substrate, wherein theplurality of light emitting elements are monolithically formed, whereinthe plurality of light emitting elements form two groups, within each ofthe two groups the light emitting elements being connected in series,wherein the plurality of light emitting elements are arranged in atwo-dimensional pattern on the substrate, and wherein each group has anarray of light emitting elements placed in a zigzag pattern, and the twogroups of light emitting element arrays are connected between twoelectrodes in parallel so that they are of opposite polarities.
 2. Thelight emitting device according to claim 1, wherein the two groups oflight emitting element arrays are alternately placed.
 3. The lightemitting device according to claim 1, wherein each of the light emittingelements and the electrodes has a substantially square, planar shape. 4.The light emitting device according to claim 1, wherein each of thelight emitting elements and the electrodes has a substantially triangle,planar shape.
 5. The light emitting device according to claim 1, whereinan overall shape of the plurality of light emitting elements and theelectrodes is substantially square.
 6. The light emitting deviceaccording to claim 1, wherein at least one of the electrodes is anelectrode for an alternate current power supply.
 7. The light emittingdevice according to claim 1, wherein the two groups of light emittingelement arrays have a common n electrode.
 8. The light emitting deviceaccording to claim 1, wherein the plurality of light emitting elementsare connected by air bridge lines.
 9. The light emitting deviceaccording to claim 1, wherein the plurality of light emitting elementsare electrically separated by sapphire which is used as the substrate.10. The light emitting device according to claim 1, wherein the twogroups have equal numbers of light emitting elements.